Sound Issue Connecting Blu-ray player

[Harshitkumar Thakker]

We have a cinema with Barco Series 2 projectors and Dolby CP500 sound processors, as well as a couple of houses with USL-JSD 80 processors and a couple of recently renovated houses with DPM100H processors. We tried to connect Blu-ray player to several of the auditoriums that had Dolby CP500 processor using the Non-Sync 1 or 2 inputs.

First was a new Blu-ray player with only one HDMI out and Digital Coax out. We connected the HDMI cable to the projector using a HDMI to DVI adapter and Digital COAX out to a Digital to Analog converter and from the Digital to Analog converter to Non-sync 1 or 2 input on the CP500. We were able to get good picture. However, for the sound, we were able to listen to the sound, but also had a loud Buzzing coming from both left and Right speakers. When we just disconnected the HDMI cable from the projector, but left the movie running, the sound was clear with no buzzing. As soon as we reconnected the HDMI cable, the buzzing came back. Even when we don't connect the HDMI cable, but just touch the metal part of the DVI connector on the projector to the DVI connector on the HDMI to DVI cable, we get the buzzing. We tried the same setup on several different auditoriums in the same building including the house with USL-JSD 80 processor, we get the same thing.

Second, we brought an older Blu-ray player with analog outputs built in, but had the same issue.

We took the same Blu-ray player to another cinema location, which also had Barco Series 2 projectors, but with Dolby CP750 processors, and we did not have any issue at that location. The sound play fine without any buzzing. So we brought one of the CP750 processors to the first location and replaced one of the CP500 with the CP750 and tried it, but ended up again with buzzing sound.

Only two houses with the DPM100H processors we are able to connect the Blu-ray players, but using blu-ray players with dual HDMI outputs, with one HDMI going to the DPM100H and the other HDMI going to the Barco Projector using the HDMI to DVI adapter.

Would anyone be able to guide me in eliminating the buzzing sound when connecting the Blu-ray player to either the CP500 or JSD-80?

Thank you in advance for your help.

[Leo Enticknap]

I'm wondering about the DAC's wall wart. I had a phono preamp that added a 60 Hz hum to the signal. Turned out to be the cheap garbage SMPS power supply that came with it. Bought a linear one and the hum went away.

[Harold Hallikainen]

Sounds like a ground loop. I suspect the D/A is ungrounded. The power supply for it probably has an EMI filter with a couple Y capacitors. These go from each side of the line to the chassis. This puts the chassis at half the line voltage with the current limited by the reactance of the capacitors. There is a safety "touch current" limit. When you connect this to an analog input, the current goes through the shield and causes a voltage drop across the shield. This voltage drop is in series with the audio. In the JSD series, we often used a differential amplifier on the analog inputs to minimize ground loop hum, but it can only attenuate so much (the common mode rejection ratio is limited). Can you run a ground wire from the chassis of the D/A to the chassis of the sound processor? That would reduce the common mode voltage on the analog inputs of the sound processor. Also, most (maybe all) have optical TOSLINK and coax inputs, so you can drive that directly, though it would be limited to stereo on the JSD-80. The JSD-100 can do Dolby decoding on TOSLINK if the DI-84 board is included. The JSD-60 can do both Dolby and DTS decoding with the DI-84 board.

You might also ensure that the projector is well grounded to the sound system rack.

Good luck!

Harold

[Harshitkumar Thakker]

Thank you Leo and Harold for your input. The DAC was an off the shelf one from BestBuy and was powered using a USB cable and so as Harold mentioned is ungrounded. We tried it both ways, powering it using it's wall wart and powering using the USB port on the Blu-ray player. Neither helped.

We also tried a Blu-ray player that had analog output, so we did not need an external DAC. That did not make any difference either.

I will try to make sure the Projector is well grounded to the Sound Rack.

Do you think, isolation transformers would help in this case?

[Harold Hallikainen]

I don't think a power isolation transformer would help. Since this happens when you connect the HDMI shield to the projector, I think the issue is the difference in ground voltage between the projector and the sound processor. The shields of the analog cables and the digital coax cable are connecting the Blu Ray chassis to the sound processor chassis without issue, so it appears the ground voltage on the D/A and the Blu Ray are ok. Audio transformers between the D/A and the sound processor would help, but good audio transformers are expensive. The COAX input of JSD processors is transformer isolated, so you could probably drive that directly from the player.

I think the simplest solution (though no guarantee it will work) is a large ground wire or strap between the projector and the sound rack to remove the common mode voltage on the analog inputs.

Good luck!

Harold

[Jim Cassedy]

Quoting Harshitkumar Thakker:

Do you think, isolation transformers would help in this case

You weren't specific as to if you meant AC power isolation transformers or audio isolation transformers.

I had a situation a couple of years ago in which I had to interface a an older Blu-Ray player with 2channel RCA outputs to a CP-750 for a couple of shows in an old theater building that I already knew was a 'ground loop nightmare'. There was buzzing (60hz) galore. I was able to solve the problem by picking up an audio isolation transformer overnight on Amazon that was intended for use in mid-range priced automobile stereo systems. It was about $25, and as a bonus, all the connecting cables already had the necessary M & F RCA plugs attached. (for 2 channels) I intended to do a frequency sweep with a scope attached to see how 'flat' they were, & how much, if any, distortion they introduced, but I never had the time. But, for our purposes at the time, they solved the problem, quickly, and at a reasonable price. Even if they did 'color' the audio a bit, it certainly wasn't obviously noticeable, unless maybe you were an audio engineer, and we got no complaints, whereas anybody with even bad hearing would have heard the obvious hum if we hadn't put that transformer in the circuit.

I used the same 'trick' again several months later when I had to interface a 16mm projector into a theater sound system at the last minute for a local film event. I now carry two of these things in my 'toolkit'' along with an assortment of cable adapters as emergency hum-killers, There are many choices available on both e-bay & Amazon. If you are considering getting one, just be sure to read the fine print in the listing, because some of these (usually the real cheap ones) only use a capacitor type circuit, and not actual transformers. Good Luck.

[Rick Cohen]

I have had similar issues with Blu-Ray players. What I do now is just rip the movie from the Blu-Ray into an MP4 file, and create my own DCP using DCP-o-matic. Much less hassle.

[Carsten Kurz]

A pair of audio transformers will probably help, at least then there is time to evaluate the issue further. These transformers are now offered by many common companies in the audio business. What you experience is a common issue as well when e.g. a notebook is connected to a projector and audio system for e.g. a presentation. So, isolation transformers are now offered by many more companies than previously. For all the other cinema audio processors, you should try to avoid an analog connection and use S/P-DIF or TOSLINK or HDMI audio, whatever is possible.

There are probably a few different ways to get rid of the problem, one could use optical/TOSLINK from a different bluray player (or through a coax->optical converter), or try to power the DA from a projector USB port (if available). One or the other might work or reduce the problem, but I think a stereo isolation transformer is the safest bet.


Can you tell us more about the projector/server combos at these locations? Some servers/projectors can take the audio from an HDMI connection.

- Carsten

[Steve Guttag]

Using audio transformers will eliminate it.

I suspect that your Blu-ray player is ungrounded (uses a 2-prong plug) and the HDMI/DVI cable will connect the player to the projector's ground, presuming it is grounded. And then you go through mystery-meat D/A adapter to a CP500...which is quasi-grounded (they don't really-really bond their audio low to chassis and you can definitely get hum out of a CP500 as a result. I ALWAYS run a ground wire to the signal ground terminal (on the green Phoenix connector in the middle used for the "remote" and to one of handy quick disconnect terminals on the chassis.

Bonding the chassis of your Blu-ray player to ground "may" help your cause too though Ideally, the projector, player, sound processor all reference the same ground and nobody has done any dumb things like floated the ground or used a neutral as a ground (they really are VERY VERY different).

[Harshitkumar Thakker]

Thank you Steve, Carsten, Jim and Rick for your suggestions. Using audio transformers did eliminate the issue. Thank you very much for your help.

[Marcel Birgelen]

In some cases, using audio transformers has been the only way to eliminate ground loops for me. They never come entirely for free though, because those audio transformers do impact your audio signal. The impact is usually most measurable in the higher frequency ranges. Using a bunch of very cheap opto-couplers should solve that issue, but would require an external power supply to drive the circuitry.

Bonding the chassis of your Blu-ray player to ground "may" help your cause too though Ideally, the projector, player, sound processor all reference the same ground and nobody has done any dumb things like floated the ground or used a neutral as a ground (they really are VERY VERY different).

Some people really qualify for the Darwin award... Besides all the other problems in such a setup, if your neutral wire breaks and you connected ground to it, you've essentially created an electrocution device.

It reminds me of situations like that time we were disassembling an old installation and literally found a cable in there with two power plugs, one at each end. It was used to "hop" from one PDU to the next in the "reverse way". The last PDU in line had its extension cord taped off...

[Steve Guttag]

The neutral/ground thing goes back a ways, at least in the USA (the only country I'm familiar with its electrical history). Outlets used to be just 2-prong and most consumer things still, often are 2-prong. Even more scary were things like electric ranges that were 3-prong with two hots and a ground and the ground was indeed used as a neutral, by design (I believe dryers would do the same thing and with them, anytime the door was open, a light bulb would come on so the ground would be a current carrying conductor).

And there is where using ground as any form of current carrying conductor is an issue (and why it is no longer allowed)...ground is only ground (potential) of there is no current flow. Via ohms law, once there is current flow, the potential at each end of the wire is not the same. So, where neutral and ground are tied together at 1st (and only the 1st) load center are neutral and ground the same. At the other end of the wires, they are most definitely NOT the same. Current flow on the neutral will have the neutral potential raise above ground. This is where, intertwining neutral and ground can cause all sorts of hums. And it doesn't have to be an outright miswire. You could have a capacitor in a device that ties neutral to ground for noise suppression be leaky (most devices now use special capacitors for such duty to avoid the potential ;-). But you could even have a neutral wire pinched on a trough cover or a device cover or poorly insulated and since it was the neutral wire that is touching ground no breakers pop but you have still set up a ground loop where ground potential is different depending on the relative positions of the various pieces of equipment and how they are individually wired to the load center.

The RDL (Radio Design Labs) makes pretty good stuff and their "TX" series of audio transformers are no exception. the TX-1A and TX-10B, for their cost do very well https://www.rdlnet.com/product.php?page=159

Jensen also is known for their audio transformers but are going to be more pricey, in my experience.

[Paul Finn]

The Altec 15015, 15095, and 15356 are also excellent audio isolation/matching transformers which can be used for various applications.

Much can be said about faulty neutral-ground electrical system connections, many intentional and unintentional, made by so called knowledgeable, experienced, licensed people, and even found in "inspected " installations. I've probably seen it all. There is nothing more important in an electrical system installation than the neutral-ground bond connection at the service entrance ONLY. From that point on, all neutral conductors are treated as though they are "hot" throughout and NEVER grounded again. The importance of following this practice (code required), without exception, cannot be overstated especially in sound and audio power installations. I've lifted every neutral conductor in 48 circuit load center panel boards to find the grounded neutrals

On this same subject, many older 240 volt three phase electrical installations were supplied from a delta connected three transformer set. To have 120/240 volt single phase power from this service, the center tap on one transformer was used to establish a neutral conductor for 120 volts from each leg of this transformer to the neutral, and 240 volts single phase between this transformer legs. As required the center tap neutral was grounded ONLY at the service neutral/ground bond. For a 240 volt single phase power source in this system, any two legs of the delta connected three transformers could be used. However the two legs connected together point on the two non-center tapped transformers is 208 volts above neutral/ground in this system (by transformer law). Many higher power digital cinema projectors require 240 volt single phase power. It is very important in these installations NOT to use the 208 volt high leg and a leg from the center tapped transformer for the power connections. ONLY use the the two legs at the ends of the center tapped winding so the 240 volt single phase circuit will be 120 volt balanced to the neutral and consequently ground in this system.

Paul Finn

[Steve Guttag]

Paul, you'll be hard pressed to find any digital projector requiring 240VAC. Most that are targeting European countries will specify 230VAC nominal with a rather wide tolerance range (200-240, for certain and likely 190-250 would be accepted but you are at the very edge with 250 possibly tipping you over faster than 190 showing itself to be a problem). In the USA, in commercial power fed via 3-phase wye, you are going to have a nominal voltage of 208...IF the nominal voltage of any leg-neutral is 120V. Voltage ranges, just in the US are going to be between 115-125 and in industrial areas, that voltage can swing a bit, depending on the time of day. A 115V L-N will have a 199 L-L output while a 125V L-N will have about 217V L-L. Other than old high-leg power about the only places I encounter 240 for cinema gear is in residential screening rooms where residential power is indeed 240V L-L

Furthermore, anyone making equipment today is going to have countries like Japan in mind and they run on lower voltage than us too so again, it will accommodate a wide range. What will happen on the lower voltage countries/area is that the current will go up. However, if you look at most any of the name plates, they are going to list the max/min voltage it can work with and the worst-case current on that range.

Using Barco as an example (since they are a Belgium company and would be planning around a 230VAC system...here is the power requirements for their "B" series projectors (Xenon):

DP2K-19B 200-240 VAC, 50-60Hz, 24A at 200 VAC
DP2K-23B 200-240 VAC, 50-60Hz, 30A at 200 VAC
DP2K-P 200-240 VAC, 50-60Hz, 30A at 200 VAC
DP4K-19B 200-240 VAC, 50-60Hz, 24A at 200 VAC
DP4K-23B 200-240 VAC, 50-60Hz, 30A at 200 VAC

Here is an NEC specification (NC2000C)

When using with a C1 connection
- Power supply for projector + power supply for lamp
200 - 240 V AC : 30A

And rounding things out...Christie (CP-2220):

A.5.1 AC Input
Voltage Range 200 - 240 VAC
Line Frequency 50Hz - 60Hz nominal
Inrush Current 45 A maximum (LVPS or LPS)
Current Consumption 23 A maximum (at 200 VAC)
Power Consumption 4500 W maximum
Current Rating of AC Input 30 A maximum (Specified Wall Breaker)

[Dave Macaulay]

"120V" single phase power is rarely 120 Volts. 117 is typical, and actual outlet voltage depends on pole transformer, main feed, and branch circuit loads. 110-120V is acceptable in practice. So 240V in single phase residential power is usually roughly 234VAC. Three phase 208 is usually close to 205V phase-phase.